PENETRATION AND COPULATION PATHS OF THE SPERMATOZOON 79 







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The four stages in polar body emergence in Rana pipiens. (7) Division spindle 

 as in egg at time of insemination. (2) Anaphase of maturation division. Stage 

 at which spindle can be seen from exterior of the egg as a black dot. Egg fixed 

 35 minutes after insemination. (5) Early telophase. Egg fixed 50 minutes after 

 insemination. (4) Polar body just forming. Egg fixed 56 minutes after insemina- 

 tion. (Courtesy, K. R. Porter, 1939, Biol. Bull., 77:233.) 



minutes for the complete invasion of the cortex. The tail piece may be 

 broken off, but the head and middle piece continue through the egg 

 substance in the general direction determined by the direction of pene- 

 tration, usually along the egg radius. This is therefore known as the 

 penetration path. Almost immediately, however, the sperm head en- 

 larges and loses its identity and is difficult to find by any known 

 cytological method. 



In the process of invading the egg, the spermatozoon takes along 

 with it some of the pigment granules of the surface (cortical) layer so 

 that a cone-shaped penetration path can be seen in sections cut in a 

 parallel plane. This path is rather straight, indicating a certain amount 

 of directional force on the part of the penetrating spermatozoon. The 

 pigment path is the only evidence of the sperm movement, since the 



